title: Dynamic slice-dependent shim and center frequency update in 3 T breast diffusion weighted imaging.
abstract: OBJECTIVE
  To demonstrate dynamic slice-dependent shim update as a simple method to reduce susceptibility-induced B0 inhomogeneity and associated pixel shift artifacts in diffusion-weighted echo planar imaging (DW-EPI) in 3 T breast imaging.
  
  
  METHODS
  Dynamic slice-dependent update of linear shim and center frequency was implemented in a dual-echo B0 mapping sequence and a DW-EPI sequence. Multi-slice axial B0 maps and diffusion-weighted images were obtained from four volunteers with both conventional and dynamic shim methods. The two shim methods were compared in terms of B0 homogeneity and EPI pixel shift artifacts.
  
  
  RESULTS
  In all volunteers the B0 maps showed significantly improved homogeneity; the left-right asymmetry was reduced by 79% and within-slice B0 standard deviation was reduced by 20% on the average. The improvements were better than what was previously reported for conventional (static) third-order shim in bilateral breast. Anatomy-referenced apparent diffusion coefficient (ADC) maps showed reduced overall image registration error obtainable with dynamic shim.
  
  
  CONCLUSIONS
  Dynamic shim is an effective method to improve B0 shimming and DW-EPI image quality in 3 T bilateral breast imaging. Magn Reson Med 71:1813-1818, 2014. © 2013 Wiley Periodicals, Inc.
authors.affiliation: GE Global Research Center, Niskayuna, New York, USA.
authors.forename: Seung-Kyun
authors.initials: SK
authors.lastname: Lee
authors.forename: Ek Tsoon
authors.initials: ET
authors.lastname: Tan
authors.forename: Ambey
authors.initials: A
authors.lastname: Govenkar
authors.forename: Ileana
authors.initials: I
authors.lastname: Hancu
mesh_terms: D000465:Algorithms; D001940:Breast / Q000033:anatomy & histology*; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: DWI; EPI; breast; dynamic shim; susceptibility